This application is based on and claims the priority under 35 U.S.C. xc2xa7119 of German Patent Application 201 01 447.5, filed on Jan. 27, 2001, the entire disclosure of which is incorporated herein by reference.
The invention relates to a method and an arrangement for monitoring the condition of roller bearings or ball bearings, and especially the outer rings of such bearings, rolling along a guide rail. The invention especially relates to monitoring the bearings of tenter clips or claws of a tenter chain running along the endless guide rails of a tentering or stretching machine.
It is generally known to use tentering or stretching machines, for example to carry out the biaxial stretching of thermoplastic synthetic polymer films. Such tentering machines typically include two endless guide rails or guide tracks, which have respective guide rail sections that respectively extend parallel to each other, diverge from each other and/or converge toward each other. The respective path of the two guide rails relative to each other determines the degree and progression of the stretching in at least one direction. The tentering machine further includes tenter chains that are each respectively made up of successive tenter clips or claws, and that run along the respective endless guide rails. Thereby, each tenter clip or claw is supported against the respective associated guide rail by a respective roller bearing or ball bearing, which are inclusively termed xe2x80x9crolling bearingsxe2x80x9d herein. Each rolling bearing includes an inner ring or race that is connected to the associated tenter clip or claw, an outer ring or race that bears and rolls against a support contact surface of the guide rail, and a set of balls or roller pins movably and supportingly arranged between the inner ring and the outer ring. The tentering machine further comprises at least one drive that is respectively connected to each respective tenter chain, so that the tenter chains carry out a progressive motion that is synchronous relative to each other along the two endless guide rails.
In the operation of such tentering machines, especially with rather high speed or fast-running tenter chains supported by rolling bearings, the rolling bearings are subject to fatigue and wear after a long period of operation. Ultimately, the result of such fatigue and wear can lead to the breakage or loss of the outer ring of any respective one or more of the bearings. This, of course, negatively influences the proper rolling support of the affected tentering clip or claw, but can also have more serious and far-reaching disadvantages. For example, the broken pieces of an outer ring of a broken rolling bearing can abrade or wear other components of the operating tentering machine, or can lead to a jamming of the tenter chain along the guide rails. This in turn requires the machine to be shut down and to be repaired and serviced, which is also reflected in the lost production output of the machine. For these reasons, there is a need in this field to be able to monitor the wear or other aspects of the functional condition of the rolling bearings, and to sense and indicate when a bearing has been worn to an unacceptable extent or when an outer ring of a bearing has been broken or lost.
In view of the above, it is an object of the invention to provide a method and an arrangement with which the functionality of the rolling bearings supporting the tenter clips or claws on the endless guide rails can be monitored during the ongoing operation of the tentering machine. The invention further aims to avoid or overcome the disadvantages of the prior art, and to achieve additional advantages, as apparent from the present specification.
The above objects have been achieved according to the invention in an arrangement comprising a guide rail and a rolling bearing including an outer ring, an inner ring, and balls or roller pins therebetween, wherein the outer ring of the rolling bearing rolls along a contact surface of the guide rail. The inventive arrangement especially further comprises a sensor or detector for sensing a physical value that is dependent on and indicative of a condition of the rolling bearing. The above objects have further been achieved according to the invention in a method of monitoring the condition of the rolling bearing in such an arrangement, by sensing or detecting the physical value, comparing the physical value to an acceptable threshold or parameter range, and then providing a fault signal in the event the detected physical value is not within the acceptable threshold or parameter range.
A significant feature of the invention is the provision of a sensing or detecting arrangement in the area at which the outer ring of a rolling bearing normally contacts the contact surface of the guide rail, whereby this sensing or detecting arrangement is adapted to sense a physical value that is dependent on and indicative of a condition of the rolling bearing as the bearing passes by this location on the guide rail. In this manner, the sensing or detecting arrangement (sometimes simply called a sensor herein) can successively sense the corresponding physical value of each one of the rolling bearings of each one of the tenter clips or claws of the tenter chain as they successively pass by the sensor location on the guide rail, during the continuous normal operation of the tentering machine.
Since the sensed physical value is dependent on and indicative of a condition of the rolling bearing that is respectively passing by the sensor, the sensor can thereby detect if the respective bearing is excessively worn, or especially if the respective bearing is already missing its outer ring, because the detected physical value would be correspondingly different from the normal or expected or acceptable range of this value. According to the invention, the physical value may, for example, be the backed-up or feedback pressure of an air flow being provided by a pneumatic air supply arrangement, or the influenced magnetic field of an electromagnetic sensor device, or the interrupted or reflected light beam of an optoelectronic sensor device.
In a preferred embodiment, the physical value to be sensed is the backed-up or feedback pressure of a supplied flow of pressurized air, as it is influenced by the passing of a respective rolling bearing. In this context, the sensing arrangement comprises a sleeve-shaped body that is arranged in a hole bored in the guide rail, in such a manner so as to form an annular ring-shaped air outlet opening annularly around the sleeve-shaped body, i.e. bounded between the outer wall of the sleeve-shaped body and an inner cylindrical wall of the bored hole in the guide rail. An air supply line is connected from a source of pressurized air to the annular air outlet. The hollow cylindrical interior of the sleeve-shaped body forms a pressure measuring or sensing channel that is concentrically surrounded by the annular air outlet opening, and that is connected by a pressure sensing or measuring line to a pressure sensor or pressure measuring arrangement, which may have any conventionally known structure and operation. Pressurized air is preferably continuously supplied to the annular air outlet, from which the pressurized air blows outwardly away from the guide rail surface in which the air pressure sensing arrangement is provided. This surface is especially the contact surface along which the rolling bearings roll.
When there is no rolling bearing at the location of the air pressure sensing arrangement at a given time, the pressure prevailing in the pressure measuring channel will be a neutral pressure, for example, the ambient surrounding air pressure, or a pressure slightly above or slightly below the ambient surrounding air pressure due to any venturi or nozzle effect of the pressurized air being ejected out of the annular air outlet opening that surrounds the pressure measuring channel. On the other hand, when an intact rolling bearing rolls over the area of the air pressure sensing arrangement, the pressurized air supplied through the annular air outlet opening will be at least partially confined or backed-up by the contact surface of the rolling bearing against the contact surface of the guide rail, which will cause a backed-up or feedback pressure in the central pressure measuring channel.
The actual pressure prevailing in the pressure measuring channel at any time is provided to the pressure sensor or pressure measuring arrangement, which in turn responsively thereto generates an electrical actual pressure signal. This electrical actual pressure signal is then compared to a nominal, rated, or desired electrical signal, or especially an acceptable signal threshold or acceptable signal value range. If the actual pressure signal deviates from the nominal or desired pressure signal by more than an acceptable tolerance value, or if the actual pressure signal falls below an acceptable pressure threshold or outside of an acceptable pressure range, then this result causes the generation or release of a fault signal that is used to automatically stop the machine, or to provide a fault indication to the operator of the machine.
In order to prevent contaminant particles from accumulating in and thereby blocking the pressure measuring channel, which would lead to a falsification of the pressure measurement result and the associated actual pressure signal, the pressure measuring channel is cleaned or flushed at regular time intervals. This cleaning process preferably comprises blowing pressurized air outwardly through the measuring channel to blow any accumulated contaminant particles out of the channel. This is achieved according to the invention by arranging a controllable multi-path valve in the pressure measuring line between the outlet of the pressure measuring channel and the pressure sensor or pressure measuring arrangement. This multi-path valve is further connected to a source of compressed or pressurized air, so that switching the valve will connect the source of pressurized air to the pressure measuring line, so as to blow pressurized air through the pressure measuring line and outwardly through the pressure measuring channel in a xe2x80x9cbackwardsxe2x80x9d flow direction opposite the normal direction for the pressure measurement.
In further embodiments according to the invention, the sensor arrangement used to sense the physical value indicative of the condition of the rolling bearing may be an electromagnetic sensing arrangement such as an eddy current sensor, or an optoelectronic sensing arrangement such as a light beam emitter and a light sensor that senses the interruption or the reflection of the light beam.
The method and arrangement according to the invention advantageously enable a continuous monitoring of the operating condition of the rolling bearings during the ongoing operation of the tentering machine. The invention makes it possible to essentially immediately react to an excessive wear or rupture failure of any one of the rolling bearings, so as to immediately take any required corrective action in the operating process of the tentering machine. Thereby, the occurrence of more-substantial damage to other components of the machine can be avoided. While the present specification describes the inventive arrangement in connection with a guide rail of a tentering machine, it should be understood that the invention similarly applies to any machine or apparatus in which a ball bearing or roller bearing rolls along a guide rail.